Effect of Red Mud and Copper Slag Particles on Physical and Mechanical Properties of Bamboo-Fiber-Reinforced Epoxy Composites

Abstract

In the present work, a series of bamboo-fiber-reinforced epoxy composites are fabricated by using red mud and copper slag particles as filler materials. A filler plays an important role in determining the properties and behavior of particulate composites. The effects of these two fillers on the mechanical properties of bamboo-epoxy composites are investigated. Comparative analysis shows that with the incorporation of these fillers, the tensile strength of the composites increases significantly, whereas the flexural strength and impact strength decrease with increase in filler content (red mud and copper slag fillers) in the epoxy-bamboo fiber composites. The density and hardness are also affected by the type and content of filler particles. It is found that the addition of copper slag filler improves the hardness of the bamboo-epoxy composites, whereas the addition of red mud filler reduces the hardness value of bamboo-epoxy composites. The study reveals that the addition of copper slag filler in bamboo-epoxy composites shows better physical and mechanical properties as compared to the red-mud-filled composites.

1. Introduction

In the recent years, for making the low-cost engineering materials the use of natural fibers in polymers composites has brought forth a lot of interest. The new environmental legislation as well as consumer demands has pressured manufacturing industries (especially automotive, packaging and construction) to search new materials that can replace the conventional nonrenewable reinforcing materials such as glass fibre, carbon fiber, and so forth [1]. The advantages of natural fibers over the traditional glass fibers are low density, good specific strength and modulus, economical viability, enhanced energy recovery, and good biodegradability [2]. There are also some disadvantages of natural fiber-reinforced polymer composites such as the incompatibility between the hydrophilic natural fibres and hydrophobic thermoplastic and thermoset matrices requiring appropriate use of physical and chemical treatments to enhance the adhesion between fibre and the matrix [3]. Generally the cellulosic fibers, like henequen, sisal, coconut fiber (coir), jute, palm, bamboo, wood, paper in their natural condition, and several waste cellulosic products such as shell flour, wood flour, and pulp have been used as reinforcement materials in different thermosetting and thermoplastic resins [4–11].

Being a conventional construction material since ancient times, bamboo fiber is a good campaigner for use as a natural fiber in composite materials. The reason that many studies focus on bamboo is because it is an abundant natural resource in Asia, and its overall mechanical properties are comparable to those of wood. Bamboo is a naturally occurring composite material, which grows abundantly in most of the tropical countries. This is one of the oldest building materials used by human kind. The attractive physical and mechanical properties that can be obtained with bamboo-fiber- reinforced composites, such as high specific modulus, strength, and thermal stability, have been well documented in the literature. Jain et al. [12] have compared the Bamboo fiber reinforced epoxy composites (BFRP)_epoxy with Bamboo-fiber-reinforced unsaturated polyester composites. (BFRP)_USP in terms of their cost and mechanical strength. Jindal[13] has observed that tensile strength of bamboo-fiber-reinforced plastic (BFRP) composite is comparatively equivalent to that of the mild steel, whereas their density is only 12% of that of the mild steel. Hence, the BFRP composites can be extremely useful in structural applications. Takagi and Ichihara [14] have studied the effect of fiber content and fiber length on mechanical properties of bamboo-fiber-reinforced green composites (BFGC). Fiber length up to 15 mm has given positive effect on tensile strength and flexural strength.

In the fiber-reinforced polymer composites, fillers play an important role. The addition of particulate fillers has shown a great promise and has been a subject of considerable interest due to the improvement in performance of polymers and their composites in industrial and structural applications due to the addition of fillers. Filler materials are used in composite materials to reduce material costs, to improve mechanical properties to some extent, and in some cases to improve processability. They also increase the properties like hardness and abrasion resistance and reduce the shrinkage. The physical and mechanical characteristics can further be modified by adding a solid filler phase to the matrix body during the composite preparation. Biswas and Satapathy [15] study the effect of red mud filler particles on the epoxy-bamboo fiber composites and epoxy-glass fiber composites. Also Biswas et al. [16] studied the effect of ceramic fillers on mechanical properties of bamboo-fiber-reinforced epoxy composites and results show that the addition of ceramic fillers in bamboo-fiber-reinforced epoxy composites enhanced the mechanical properties of the composites. Although a great deal of work has been published on the effect of various types and content of fillers on polymer composites, the potential of ceramic-rich industrial wastes for such use in polymeric matrices has rarely been explored. Industrial development over the last decades has generated huge amounts of toxic and hazardous inorganic waste like, fly ash, cement by pass dust, copper slag, red mud, and so forth, which contain appreciable amounts of hazardous elements.

Production of alumina from bauxite by the Bayer's process is associated with the generation of red mud as the major waste material in alumina industries worldwide. Depending upon the quality of bauxite, the quantity of red mud generated varies from 55 to 65% of the bauxite processed [17]. The enormous quantity of red mud discharged by these industries poses an environmental and economical problem. Red mud, as the name suggests, is brick red in colour and slimy having average particle size of about 80–100 μm. It comprises of the iron, titanium, and the silica part of the parent ore along with other minor constituents. Depending on the source, these residues have a wide range of composition: Fe₂O₃ 20–60%, Al₂O₃ 10–30%, SiO₂ 2–20%, Na₂O₂ 10%, CaO 2–8%, and TiO₂ traces 2–8%. Copper slag is produced during matte smelting and conversion steps in the pyro-metallurgical production of copper. During matte smelting, two separate liquid phases, copper-rich matte (sulphides) and slag (oxides) are formed. It has been estimated that for every tonne of refined copper produced, about 2.2 tonne of slag is generated and every year, approximately 24.6 million tonne of slag is generated in copper production worldwide. Slag containing <0.8% copper is either discarded as waste or sold as products with properties similar to those of natural basalt (crystalline) or obsidian (amorphous). Copper slag having average particle size of about 80–100 μm. The composition of the copper slag is as follows: Fe₂O₃ 35.3%, SiO₂ 36.6%, CaO 10%, Al₂O₃ 8.1%, CuO 0.37%, MgO 4.38%, Na₂O 0.47%, K₂O 3.45%, PbO 0.12%, Zn 0.97%, and Cu 0.24%. The objectives of this study were to investigate the physical and mechanical properties of particulate (red mud and copper slag) filled epoxy-bamboo fiber hybrid composites and present the comparison between the effect of red mud and copper slag filler on bamboo-epoxy composites.

2. Preparation of Composites

The filler composites of four different compositions are prepared for this study. Bamboo fiber was collected from local supplier and is used as the common reinforcing phase in all the four compositions. The bamboo fiber has an elastic modulus 1.9 GPa and possesses a density of 1.32 g/cm³. Epoxy resin (Elastic modulus 3.42 GPa, density 1.36 g/cm³), manufactured by Ciba Geigy and locally supplied by Northern Polymers Ltd. New Delhi, India, is the matrix material. Here the red mud and copper slag are used as filler materials. The composites are made by conventional hand lay-up technique. The low temperature curing epoxy resin and corresponding hardener (HY951) are mixed in a ratio of 10 : 1 by weight as recommended. After that red mud and copper slag fillers are mixed in the epoxy resin before the bamboo fiber is reinforced in the matrix, the composites are prepared in two different sets. In first set, the red mud, (0, 5, 10, and 15 wt.%) is used as filler materials and mixed in the epoxy resin before the bamboo fiber is reinforced in the matrix. In second set, copper slag (0, 5, 10, and 15 wt.%) is used as a filler materials and mixed in the epoxy resin before the bamboo fiber is reinforced in the matrix. For all the composition, bamboo fiber-loading (weight fraction of bamboo fiber in the composite) is kept fixed, that is, 45 wt.% of bamboo fiber. The castings are put under load for about 24 h for proper curing at room temperature. Specimens of suitable dimension are cut using a diamond cutter for physical, mechanical characterization, and erosion testing.

3. Physical and Mechanical Characterization

3.1. Density

The theoretical density of the composite materials in terms of weight fraction can easily be calculated as in the following equation given by Agarwal and Broutman [18]:

\begin{matrix} ρ_{ct} = \frac{1}{(W_{f} / ρ_{f}) + (W_{m} / ρ_{m})} . \end{matrix}

In this equation, W and ρ represent the weight fraction and density of the fiber and matrix materials. Equation (1) is suitable only for two phase composite materials, but in the present investigation the composites consist of three components, that is, matrix, fiber and particulate filler. Therefore, the theoretical density of the theses composites can be calculated easily by using the following modified form of (1) written as

\begin{matrix} ρ_{ct} = \frac{1}{(W_{f} / ρ_{f}) + (W_{m} / ρ_{m}) + (W_{p} / ρ_{p})}, \end{matrix}

(2)

where the suffix “ρ” indicates the particulate filler materials.

Whereas the actual density (ρ_ce) of the composites can be determined experimentally by using simple water immersion technique. The volume fraction of voids (V_v) in the composites is calculated using the following equation:

\begin{matrix} V_{v} = \frac{ρ_{ct} - ρ_{ct}}{ρ_{ct}} . \end{matrix}

3.2. Micro-Hardness

Micro-hardness measurement is done using a micro-hardness tester equipped with a square-based pyramidal (angle 136° between opposite faces) diamond indenter by applying a load of 10 N.

3.3. Tensile Test

The tensile test is performed on flat specimens. During the tensile test, a uniaxial load is applied through both ends of the specimen. The ASTM standard test method for tensile properties of fiber resin composites has the designation D 3039-76. The length of the test section should be 200 mm. The tensile test is performed in the universal testing machine (UTM) Instron 1195, and results are analyzed to calculate the tensile strength of composite samples.

3.4. Flexural Strength

The flexural strength is calculated by three point bend test, and the data is recorded during the test. The flexural strength (F.S) of any composite specimen is determined using the following equation. The test is conducted as per ASTM standard (D2344-84) using the same universal testing machine (UTM)

\begin{matrix} F . S = \frac{3 P L}{{2 b t}^{2}}, \end{matrix}

where P is maximum load, b the width of specimen and t the thickness of specimen, and L the span length of the sample.

3.5. Impact Test

Low velocity instrumented impact tests are carried out on composite specimens. The tests are done as per ASTM D 256 using an impact tester. The pendulum impact testing machine ascertains the notch impact strength of the material by shattering the V notched (45°) specimen with a pendulum hammer, measuring the spent energy, and relating it to the cross section of the specimen. The standard specimen for ASTM D 256 is 60 mm × 10 mm × 4 mm and the depth under the notch is 2 mm.

4. Results and Discussions

4.1. Effect of Filler Content on Void Faction of Particulate Filled Epoxy-Bamboo Fiber Composites

Determining the properties of the composites, density is the most important factor. Density generally depends upon the relative proportion of the matrix and the reinforcing materials. The theoretical and measured densities along with the corresponding volume fraction of voids for red mud filled and copper filled epoxy-bamboo fiber composites are presented in Tables 1 and 2. It is noticed that the density calculated theoretically using (1) is not in agreement with the experimental calculated density value. Therefore, the difference between the theoretical and experimental density value is the measure of the voids and pores present in the composites.

Table 1:

Density and void fraction of red mud filled short epoxy-bamboo fiber composites.

Designation	Composition	Theoretical density (g/cm³)	Experimental density (g/cm³)	Voids fraction (%)

EBR-1	Epoxy + 45 wt.% Bamboo fiber + 0 wt.% red mud	1.17	1.15	1.71
EBR-2	Epoxy + 45 wt.% Bamboo fiber + 5 wt.% red mud	1.21	1.18	2.48
EBR-3	Epoxy + 45 wt.% Bamboo fiber + 10 wt.% red mud	1.23	1.17	4.88
EBR-4	Epoxy + 45 wt.% Bamboo fiber + 15 wt.% red mud	1.25	1.16	7.20

EBR: Red mud filled Bamboo fiber reinforced Epoxy composites.

Table 2:

Density and void fraction of copper slag filled short epoxy-bamboo fiber composites.

Designation	Composition	Theoretical density (g/cm³)	Experimental density (g/cm³)	Voids fraction (%)

EBC-1	Epoxy + 45 wt.% Bamboo fiber + 0 wt.% copper slag	1.17	1.15	1.71
EBC-2	Epoxy + 45 wt.% Bamboo fiber + 5 wt.% copper slag	1.27	1.21	4.72
EBC-3	Epoxy + 45 wt.% Bamboo fiber + 10 wt.% copper slag	1.34	1.25	6.72
EBC-4	Epoxy + 45 wt.% Bamboo fiber + 15 wt.% copper slag	1.49	1.38	7.38

It is seen from Tables 1 and 2 that the volume fraction of voids increases with increasing the filler concentration in the epoxy-bamboo fiber composites. In case of 0 wt.% red mud and copper slag filled epoxy-bamboo fiber composite, the volume fraction of voids is less. However, with the addition of filler materials, more voids are found in the composites. As the filler content increases from 5 wt.% to 15 wt.%, the volume fraction of voids is also found to be increasing proportionately. The composites filled with 15 wt.% of red mud and copper slag filled epoxy-bamboo fiber composites showd the maximum volume fraction of voids as compare to the others composites. Hence, based up on the above analysis, it is clearly demonstrated that with increase in filler concentration the void content of the composites goes on increasing. On comparison of red mud and copper slag filled epoxy-bamboo fiber composites, it is seen that the composites filled copper slag filler shows the higher values of voids as compared to the red mud filled composites. This is due to the higher density of the copper slag fillers as compared to the red mud filler.

The mechanical performance of the composites is generally influenced by the presence of voids, and the estimation of the quality of the composites is based upon the knowledge of void contents in the composites. The air-filled cavities formed inside the composite is known as porosity, and it is, often unavoidable part in all the composites during the fabrication process. The void may be originated during the mixing and integration of two or more different material parts. Higher void contents usually mean lower fatigue resistance, greater susceptibility to water penetration, and weathering [18]. It is understandable that a good composite should have fewer voids. However, presence of void is unavoidable in composite making particularly through hand-lay-up route.

4.2. Effect of Filler Content on Hardness of Particulate Filled Epoxy-Bamboo Fiber Composites

Surface hardness of the composites is considered as one of the most important factors that govern the nature and properties of the composites. The measured hardness values of both the red mud and copper slag filled and unfilled epoxy-bamboo fiber composites are shown in Figure 1. It is seen that in case of red mud filled composites, the hardness value decreases with increase in the filler contents.

Figure 1:

Variation of Micro-hardness with red mud and copper slag filler percentage.

Whereas in case of copper slag, the hardness value increases with increases in the fillers contents. In case of hardness test, a compression or pressing stress is in action. So the matrix phase and the solid filler phase would press together and touch each other more significantly. Thus the interface can transfer pressure more effectively although the interfacial bond may be poor.

4.3. Effect of Filler Content on Tensile Strength of Particulate Filled Epoxy-Bamboo Fiber Composites

Tensile properties of red mud and copper slag filled epoxy-bamboo fiber composites were studied. Tensile strength of the bamboo-epoxy filled with red mud and copper slag filler content ranged from 0 wt.% to 15 wt.% is shown in Figure 2. It is seen that the tensile strength of all the composites increases with increase in the both the fillers contents.

Figure 2:

Variation of Tensile strength with red mud and copper slag filler percentage.

However, the composite filled with 5 wt.% of red mud filler contents shows the lower tensile strength value as compared to 0 wt.% of red mud filled epoxy-bamboo fiber composite. The decreased in tensile strength with 5 wt.% of red mud filler content is due to the poor adhesion between the fiber, filler, and the matrix, because without proper adhesion at higher loads reinforcements promote void formation. The particle loading and particle size, the particle, fiber and matrix interfacial adhesion significantly affects the strength of the composites. The effective stress transfer is the most important factor, which leads to the strength of composites materials. When the bonding between the particles and matrix is poor, the stress transfer at the particle/polymer interface is insufficient. Therefore, discontinuity in the form of debonding exists because of non-adherence of particle to polymer. Due to this (debonding), the particle cannot carry any load and the composite strength decreases with increasing particle loading [19]. However, for composites containing well-bonded particles, addition of particles to a polymer will lead to an increase in strength of the composites. So due to the good bonding of red mud and copper slag fillers particles with matrix, the tensile strength of all the composites increases with increases in the both the fillers contents.

4.4. Effect of Filler Content on Flexural Strength of Particulate Filled Epoxy-Bamboo Fiber Composites

Figure 3 shows the flexural strength of red mud and copper slag filled epoxy-bamboo fiber composites obtained experimentally from three bend tests.

Figure 3:

Variation of Flexural strength with red mud and copper slag filler percentage.

It is observed that the epoxy-bamboo fiber composites filled with 5 wt.% and 10 wt.% of red mud and copper slag particles have the lower value of flexural strength as compared to the 0 wt.% of red mud and copper slag filled epoxy-bamboo fiber composites, whereas the composite filled with 15 wt.% of red mud and copper slag particles shows the higher value of flexural strength as compared to the 0 wt.% of red mud and copper slag filled bamboo-epoxy composites. This increase in the flexural strength may be related to the presence of red mud and copper slag particulates located at the interface of the fiber and matrix. The reduction in the flexural strengths of the composites with filler content is probably caused by an incompatibility of the particulates and the epoxy matrix, leading to poor interfacial bonding. The lower values of flexural properties may also be attributed to fiber-to-fiber interaction, voids, and dispersion problems. Also it is observed that the cooper slag filled composites show the better flexural strength as compare to the red mud filled bamboo epoxy composites.

4.5. Effect of Filler Content on Impact Strength of Particulate Filled Epoxy-Bamboo Fiber Composites

The ability of a material to resist breaking under a sudden loading or the ability of material to withstand the fracture under the action of high speed stress is known as the impact strength. In the polymer materials, the impact strength is the most widely specified mechanical property [20]. The impact performance of particulate filled fiber-reinforced composites depends on many factors like the nature of the constituent, the filler, fiber, matrix interface, the fabrication, geometry of the composite, and the test conditions. The impact failure of a composite occurs by factors like matrix fracture, and fibre/matrix debonding. The applied load transferred by shear to fibres may exceed the fibre/matrix interfacial bond strength and debonding occurs. When the stress level exceeds the fibre strength, fibre fracture occurs, which involves energy dissipation [21].

Figure 4 shows the impact strength of both the red mud and copper slag filled epoxy-bamboo fiber composites. The value of impact strength shows a reduction with the addition of both the red mud and copper slag in epoxy-bamboo fiber composites. It is seen that with the increase in the both the filler contents, the impact strength of all the composites decreases. Increased filler contents in the matrix resulted in composites becoming stiffer and harder. This will reduce the composite's resilience and toughness and lead to lower impact strength.

Figure 4:

Variation of Impact Strength with red mud and copper slag filler percentage.

5. Conclusions

This study shows that successful fabrication of epoxy-bamboo fiber composites filled with red mud and copper sag particles is possible. Addition of these fillers modifies the physical (density and hardness) and mechanical properties (tensile, flexural, and impact strength) of the bamboo-epoxy composites. The tensile strength of both the red mud and copper slag filled composites increases with increase in the filler contents, whereas the flexural strength and impact strength of both the filled composites decrease with increase in the fillers filler contents. The micro-hardness and density of the composites are also greatly influenced by the type and content of fillers. In case of micro-hardness, with the addition of copper slag fillers the hardness value of epoxy-bamboo fiber composites increases, whereas with the addition of red mud filler the hardness value decreases with increase in the filler contents. Hence, while fabricating a composite of specific requirements, there is a need for the choice of appropriate filler material and for optimizing its content in the composite system.

Footnotes

Acknowledgment

The corresponding author is grateful to Department of Science and Technology, Govrnment of India for providing the financial support for this research work under the Research Project Ref. no. SR/FT/ET-026/2009.

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